There are many uses for thin, e.g., one inch thick, veneers of granitic stone with a natural split “rock face”, that is, a surface that has been exposed in a splitting process. Such a stone surface will typically be somewhat irregular, although approximately planar. Such natural rock surfaces are desired, for example, in architectural facings.
It is well-known to split granitic stone slabs into smaller pieces, typically by employing a press having opposed splitting wedges. Commonly the splitting tools components are each made up of a series of aligned wedges that are separately adjusted so as to contact the slab along the intended splitting line in as many places as possible. The wedges are shaped to define 90° cutting edges, aligned symmetrically along the desired splitting plane. The aligned opposed wedges are then forced into the stone slab by one or more hydraulic rams, splitting the slab into two. However, this process is limited in that it is ordinarily only possible to split pieces from a granitic stone slab the width of which are at least approximately one-half the thickness of the slab. For example, from a slab eight inches thick pieces each approximately four inches wide can be split using the prior art process, but it is not possible to split thin veneers using this prior art process. In the prior art such thin rock-faced veneers can only be cut from a rock-faced slab in a sawing process, which is very time-consuming and accordingly costly.
It would be highly desirable to provide a method for processing slabs of granitic stone to yield thin rock-faced veneers, which would be considerably faster than sawing and far less costly. The present invention provides such a process. The process of the invention, as described below, could also be used to trim monumental pieces to their approximate final shape before finishing.
Prior art references located in a search of the present invention include the following:
Lindberg U.S. Pat. No. 1,096,849 discloses an apparatus for breaking diamonds wherein the individual diamond to be cut is used as a pattern to fabricate cutting blades that exactly match the contours of the individual diamond. This would be very costly in practice.
Derbyshire U.S. Pat. No. 1,162,685 teaches a stone breaking machine intended for breaking “Belgian blocks” into smaller pieces. The machine comprises a steam hammer fitted with bits opposed to one another along a desired cutting line; the bits may be both sharp, both blunt, or one sharp and one blunt (see lines 61-63) and appear to be symmetrical about the desired cutting line.
Koch U.S. Pat. No. 2,049,704 shows a brick splitting mechanism wherein the bricks are split by opposed splitting blades having chisel-type beveled cutting edges.
Sunada U.S. Pat. No. 3,026,865 shows a stone cutter intended specifically for cutting of “soft stone such as volcanic rock, sand stone and the like” (Col. 1, lines 10-11). The Sunada cutter comprises an arcuate cutting blade forced into the stone from one side.
Cox et al U.S. Pat. No. 3,120,842 shows an equalizer for a shear for rock wherein a number of small elements, such as ball bearings or the like, are disposed in upper and lower chambers so as to support assemblies of individual cutting bits; as the assemblies of bits are brought into contact with a slab, the elements move in the chamber so that the cutting bits each contact the slab along a desired cutting line. The bits may be sharp or rounded.
Hillberry et al U.S. Pat. No. 3,901,423 shows a method for fracturing crystalline materials, such as rods of semiconductor material. A tensile load is applied to opposed ends of the rod, and a wedge is forced into a precut notch on one side of the rod, while a spherical support is disposed on the opposite side of the rod.
Lechner U.S. Pat. No. 7,107,982 shows a brick cutting machine having opposed upper and lower blades; the upper blade may be offset from the lower blade where it is desired to split the brick other than perpendicular to its faces. See FIG. 6, and discussion thereof at col. 5, lines 3-16.
Karau et al U.S. Pat. Nos. 7,766,002, 8,028,688 and 8,136,515 show apparatus for simultaneously splitting and “pitching” (that is, beveling the edges of) concrete blocks, comprising a plurality of parallel blades.
U.S. Pat. Nos. 4,699,564 and 6,073,621 to the present inventor disclose improvements in equipment useful in stone cutting, but are not directly relevant to the technique of splitting stone disclosed herein.
Finally, German patent DE 10313422 shows a machine for splitting slate blocks following the “natural lamination” of the slate. FIG. 2 appears to show a symmetrically-beveled blade being forced into the slate opposite an anvil. It will be apparent to those of skill in the art, and as noted above, that splitting such “laminated” stone, i. e., stone exhibiting a structure defining planes of weakness, is a different matter than splitting slabs of granitic stone having no clearly defined splitting planes.
Accordingly, it is an object of the invention to provide a method for processing slabs of hard, non-“laminated”, granitic stone into thin “rock-faced” veneers, that is, members having thickness substantially less than half the thickness of the slab.